Construction of a Test Track

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Colin Parks
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Re: Construction of a Test Track

Postby Colin Parks » Mon Jul 09, 2018 11:19 am

Hello Phillip,

One of the matters that you have raised is that of rail movement in track bases. From what you describe, the track bases hold the rails - but not too tight. That sounds like the ideal situation, as long as the track gauge is consistent.

Reflecting on my use of functional plastic chairs has led me to believe that there might be very little chance of rail expansion or contraction movement. The chairs grip the rail tightly once fixed down. A while ago, I had posted a picture of curved bases of chairs threaded onto a rail. It now seems as if the action of fixing and flattening the curved chair bases has effectively produced hundreds of tiny rail 'clamps', which do not easily allow the rails to slide sideways!

Colin

Philip Hall
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Re: Construction of a Test Track

Postby Philip Hall » Mon Jul 09, 2018 1:59 pm

Colin,

Thanks for an encouraging comment! My principle concern was whether rail section produced many years before the FastTrack bases were even thought of would properly fit them. It does (much relief all round!) and the very easy fit makes it quick to assemble track as a result. It was a bargain purchase (saved me a huge amount of money) and ideal for my application as I did not want to use steel in an outbuilding. It’s old style nickel silver of course, not hi-hi which I would have quite liked for its improved appearance, but apart from the money I did not have the problems reported on here of chairs being forced apart by a web that is too thick.

I think the fact that the chairs are accurately moulded onto the sleeper panels has a lot to do with the consistent gauge, even if a touch wide. Individual sleepers and chairs are not ready aligned when done singly. Now the next experiment will be the PCB track in the hidden areas, because being solidly soldered might need more expansion gaps. But first I have to buy the table saw to cut up some sleepers...

Philip

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Le Corbusier
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Re: Construction of a Test Track

Postby Le Corbusier » Mon Jul 09, 2018 6:51 pm

Colin Parks wrote:
Reflecting on my use of functional plastic chairs has led me to believe that there might be very little chance of rail expansion or contraction movement. The chairs grip the rail tightly once fixed down. A while ago, I had posted a picture of curved bases of chairs threaded onto a rail. It now seems as if the action of fixing and flattening the curved chair bases has effectively produced hundreds of tiny rail 'clamps', which do not easily allow the rails to slide sideways!

Colin


Hi Colin,

I had the same curve to the bases of my chairs and like you the fixing process with the Butanone has fixed them down flat. However as I fixed each rail section, once it had set I pulled the rail back and forth along the length using a pair of pliers. In every case I got it to slide within the chairs freely.

Tim
Tim Lee

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Colin Parks
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Re: Construction of a Test Track

Postby Colin Parks » Mon Jul 09, 2018 9:27 pm

Well Tim, you have the fortune not to have droppers which prevent sliding the rail through the chairs in the way you describe (as in my case and for anyone else who is not using radio controlled loco's). Although the droppers I have added are a loose fit the holes through the baseboard, there is only approx. 1 mm clearance.

The Hi-nickel rail I have used does have a thicker web than the prototype rail section, which contribtues to a tighter grip on the rail by the plastic chairs. The reason I think it is a question of rail-not-matching chair and not tool or mould wear is because I have used Exactoscale chairs from across three dfferent time periods: very old ones (with longer keys), four year-old ones and some supplied this year - plus several hundred C&L chairs. They all are tight to thread onto the rail and have concave bases once threaded.

Of course, once the current hot spell has passed, all these problems will fade away - until next time...

Colin

Tony Wilkins
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Re: Construction of a Test Track

Postby Tony Wilkins » Mon Jul 09, 2018 9:41 pm

Colin Parks wrote:The Hi-nickel rail I have used does have a thicker web than the prototype rail section
Colin

Don’t they all? Its just a question of by how much!
Regards
Tony.

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Le Corbusier
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Re: Construction of a Test Track

Postby Le Corbusier » Mon Jul 09, 2018 9:57 pm

Colin Parks wrote:Well Tim, you have the fortune not to have droppers which prevent sliding the rail through the chairs in the way you describe (as in my case and for anyone else who is not using radio controlled loco's). Although the droppers I have added are a loose fit the holes through the baseboard, there is only approx. 1 mm clearance.

Will endeavour to engage brain next time :thumb ;)
Tim Lee

Phil O
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Re: Construction of a Test Track

Postby Phil O » Thu Jul 12, 2018 2:14 pm

Hi Colin,

As long as you're not using long lengths of rail or there are not large variations in temperature a mil or so is ample.

Phil

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Colin Parks
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Re: Construction of a Test Track

Postby Colin Parks » Thu Jul 12, 2018 9:50 pm

Hello Phil,

By the time I have eradicated those funtional plastic fishplates that can be taken out, there will be about the amount of gap that you suggest between the rails. To be clear, there has only been one location and one rail that has distorted due to the recent hot weather and removing one fishplate created a gap of over 0.5mm.

The temperature range in the place where the test track has been over the course of its construcion has been, from about 5C to no more than 29C.

All the best,

Colin

Phil O
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Re: Construction of a Test Track

Postby Phil O » Sun Jul 15, 2018 8:45 am

If I have done the maths correctly and I wouldn't like to put a bet on it, I get 4mm of expansion for a metre over the temperature range you have given. It's been a long time since I had to do it.

Phil

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Le Corbusier
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Re: Construction of a Test Track

Postby Le Corbusier » Sun Jul 15, 2018 9:21 am

Phil O wrote:If I have done the maths correctly and I wouldn't like to put a bet on it, I get 4mm of expansion for a metre over the temperature range you have given. It's been a long time since I had to do it.

Phil

presumably there should be an element of contraction to this as the rail will have been laid most likely at a mid temperature?

4mm is still quite a lot .... presumably that would be 2mm over 500mm and 1mm over 250mm (so scale 60ft rail lengths).
Tim Lee

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stephenfreeman
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Re: Construction of a Test Track

Postby stephenfreeman » Sun Jul 15, 2018 9:55 am

So scale rail section results in scale expansion? Perhaps another reason for following prototype practice more closely?

But can you scale heat??? ;)
Stephen Freeman
Bespoke Finescale Trackwork and Semaphore Signals 7mm to 4mm scales
http://www.borg-rail.com or http://www.tracknsignals.co.uk

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Colin Parks
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Re: Construction of a Test Track

Postby Colin Parks » Sun Jul 15, 2018 11:57 am

Hello Phil, prototype data would suggest that a steel rail 18.5 m long requires a maximum expansion gap of 14.3 mm: https://pwayblog.com/2016/03/04/maximum ... nsion-gap/ It appears that both heat and expansion are not scaleable, so for steel rail the expansion range is 0.77 mm (rounded to two decimal places) per metre, given the temperature range of the UK climate.

...and of course the real railways do not use nickel silver rails!

Alan Turner
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Re: Construction of a Test Track

Postby Alan Turner » Sun Jul 15, 2018 2:06 pm

Ni-Silver will expand about 15% more than Steel.

For temperature difference of 10 DegC then for a 500mm long rail the gap should be 0.08mm for Ni-Silver and 0.07mm for steel based on the above criteria.

It's a linear relationship so double the temperature range double the gap likewise the rail length.

EDIT: Stainless steel expands more than Ni-Silver, about 25% more.

regards

Alan

Phil O
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Re: Construction of a Test Track

Postby Phil O » Sun Jul 15, 2018 5:41 pm

Le Corbusier wrote:
Phil O wrote:If I have done the maths correctly and I wouldn't like to put a bet on it, I get 4mm of expansion for a metre over the temperature range you have given. It's been a long time since I had to do it.

Phil

presumably there should be an element of contraction to this as the rail will have been laid most likely at a mid temperature?

4mm is still quite a lot .... presumably that would be 2mm over 500mm and 1mm over 250mm (so scale 60ft rail lengths).



Tim,

You're correct in your assumptions, if the track was laid at the time that the temperature was in the middle of Colin's temperature range, then there would be up to 2mm of expansion or contraction over the full temperature range. The expansion or contraction is proportional to the length of rail or whatever and the temperature range.

Phil.

Tony Wilkins
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Re: Construction of a Test Track

Postby Tony Wilkins » Sun Jul 15, 2018 6:02 pm

Coefficient of expansion figures seem to vary between sources, but the following seem typical. All figures x 10 to the - 6 mm per degree c.
The general range appears to be 11 - 12 for steel, 18 for Nickel or German silver and stainless steel varies depending on the grade.
For comparison wood is typically 30 across the grain but only 3 with the grain (what this does to plywood is food for thought) but plastics are far worse at 70 or more depending on type. I can vouch for the expansion of plastic from personal experience as the platform for Green Street grows longer than its space on the baseboard during hot weather unless rigidly fixed down.
Regards
Tony.

Alan Turner
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Re: Construction of a Test Track

Postby Alan Turner » Sun Jul 15, 2018 8:10 pm

stephenfreeman wrote:So scale rail section results in scale expansion? Perhaps another reason for following prototype practice more closely?

But can you scale heat??? ;)


The scale section is irrelevant. A solid bar of steel the same length would expand the same.

Regards

Alan

Alan Turner
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Re: Construction of a Test Track

Postby Alan Turner » Sun Jul 15, 2018 8:24 pm

Colin Parks wrote:Hello Phil, prototype data would suggest that a steel rail 18.5 m long requires a maximum expansion gap of 14.3 mm: https://pwayblog.com/2016/03/04/maximum ... nsion-gap/ It appears that both heat and expansion are not scaleable, so for steel rail the expansion range is 0.77 mm (rounded to two decimal places) per metre, given the temperature range of the UK climate.

...and of course the real railways do not use nickel silver rails!



You need to be aware that the prototype uses a temperature range of 70 Dec C. I doubt that your layout will be subject to such a range ( unless it's an outdoor layout).

Regards

Alan

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Colin Parks
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Re: Construction of a Test Track

Postby Colin Parks » Sun Jul 15, 2018 10:38 pm

Hello Alan,

Yes, I was aware of the tempreature range of -17C to 53C is used in the calculation of expansion of prototype UK steel rail, but forgot to include the information in my reply. Unless I have totally misunderstood the theory, it appears to me that a steel P4 rail 1 metre long would expand by no more than a 1 metre section of prototype rail subjected to the same thermal conditions i.e. no more than 0.77 mm from one extreme to the other of the temperature range.

Hello Tony,

Looking at the coefficient values for other materials, it would seem that for anything to function properly across the temperature range which a model railway might be subjected to, there must be some allowance for the expansion of wood, plastics and metals built into the design. From now on, I shall be allowing 1 mm of expansion/contraction per linear metre of rail over the expected temperature range of 5C - 30C for the track.

Hello Phil,

While coefficient of linear expansion for steel is as Tony Wilkins has indicated from the sources I have looked at, I have not been sure what it would be for nickel-silver alloys, but certainly more than that of steel. However, I do not understand how you arrive at the figure of 4 mm expansion per metre (for nickel-silver alloy?), which seems to be rather a lot!

Colin

Alan Turner
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Re: Construction of a Test Track

Postby Alan Turner » Mon Jul 16, 2018 7:35 am

Colin Parks wrote:Hello Alan,

Yes, I was aware of the temperature range of -17C to 53C is used in the calculation of expansion of prototype UK steel rail, but forgot to include the information in my reply. Unless I have totally misunderstood the theory, it appears to me that a steel P4 rail 1 metre long would expand by no more than a 1 metre section of prototype rail subjected to the same thermal conditions i.e. no more than 0.77 mm from one extreme to the other of the temperature range.

Hello Phil,

While coefficient of linear expansion for steel is as Tony Wilkins has indicated from the sources I have looked at, I have not been sure what it would be for nickel-silver alloys, but certainly more than that of steel. However, I do not understand how you arrive at the figure of 4 mm expansion per metre (for nickel-silver alloy?), which seems to be rather a lot!

Colin


0.77mm - obviously depends on the steel used but I would suggest 0.98mm more likely (Coeff = 14, Delta T = 70).

Ni_Silver - For Ni-S I calculate 1.26mm (coeff = 18, Delta T = 70).

Stainless steel has a greater expansion than Ni-S.

regards

Alan

Phil O
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Re: Construction of a Test Track

Postby Phil O » Mon Jul 16, 2018 6:18 pm

Hi Colin,

I did say my maths on expansion was a little rusty, it's over 40 years since I last needed to work out the expansion of anything. I used 5C as the temperature at which the rail was laid to give the maximum expansion range, whereas I suspect you probably laid the track 10 to 15 degrees warmer than that and a coefficient of 16.7.

Phil.

Alan Turner
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Re: Construction of a Test Track

Postby Alan Turner » Mon Jul 16, 2018 7:14 pm

Phil O wrote:Hi Colin,

I did say my maths on expansion was a little rusty, it's over 40 years since I last needed to work out the expansion of anything. I used 5C as the temperature at which the rail was laid to give the maximum expansion range, whereas I suspect you probably laid the track 10 to 15 degrees warmer than that and a coefficient of 16.7.

Phil.


I can't see a temperature difference of more than 25deg for an inside environment so a coeff of 16.7 would give for 1m a total movement of 0.41 mm.

Regards

Alan

Phil O
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Re: Construction of a Test Track

Postby Phil O » Tue Jul 17, 2018 12:53 pm

Alan Turner wrote:
Phil O wrote:Hi Colin,

I did say my maths on expansion was a little rusty, it's over 40 years since I last needed to work out the expansion of anything. I used 5C as the temperature at which the rail was laid to give the maximum expansion range, whereas I suspect you probably laid the track 10 to 15 degrees warmer than that and a coefficient of 16.7.

Phil.


I can't see a temperature difference of more than 25deg for an inside environment so a coeff of 16.7 would give for 1m a total movement of 0.41 mm.

Regards

Alan



Alan,

I was using the extremes of the temperature range that Colin mentioned a few posts further up the thread, where he said that the temperature where the layout lives is subject to a variation from 5C to not more than 29C. I also noted that a) I doubt that the track was laid when the room temperature was at 5C and was more likely to be 10C to 15C warmer and b) my maths was likely to be in error as it's over 40 years since I last had to work out the expansion of anything, from your result, it would appear that I got the decimal point in the wrong place. Thanks for pointing out my error.

Phil.

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Colin Parks
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Re: Construction of a Test Track

Postby Colin Parks » Tue Jul 17, 2018 6:49 pm

Hi Phil,

You were right about the temperature in the workshop where the test track is being constructed as being in the 15-20C range.

Given all the information on expansion that has come light here, I shall iam to allow a 0.5 mm gap per 500 mm (nickel-silver) rail length, or 0.25 mm per scale track panel length of 240 mm. With the cosmetic rail joints widened accordingly, it might even give the characteristic clickety-clack sound as the wheels pass over the joints!

Colin

Tony Wilkins
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Re: Construction of a Test Track

Postby Tony Wilkins » Tue Jul 17, 2018 10:10 pm

Colin Parks wrote:Hi Phil,

You were right about the temperature in the workshop where the test track is being constructed as being in the 15-20C range.

Given all the information on expansion that has come light here, I shall iam to allow a 0.5 mm gap per 500 mm (nickel-silver) rail length, or 0.25 mm per scale track panel length of 240 mm. With the cosmetic rail joints widened accordingly, it might even give the characteristic clickety-clack sound as the wheels pass over the joints!

Colin

Hi Collin.
One does of course need to be aware of the ambient temperature (and its possible effects) when laying / constructing track and I would suggest your figures are about right. As mentioned in my Turnout construction thread, as a rule of thumb I generally use my thumb nail as a convenient check for the gaps between the crossing rails and closure rails for my soldered turnouts. The question is, do I have a British Standard thumb?
Regards
Tony.

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Colin Parks
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Re: Construction of a Test Track

Postby Colin Parks » Wed Jul 18, 2018 9:59 pm

Hello Tony,

Yes, I remember your 'rule of thumb' gap calculation! Here is a video which might be of interest - especially at 2: 40 secs or so https://www.youtube.com/watch?v=qoRni1z9PjI

Regards,

Colin


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